iPhone 4 needs updated iOS for Skype

Need to install Skype on iPhone 4. Cannot as Skype needs iOS 8 or higher and iPhone has 7.1.2. Tried to update iPhone iOS but says current. An alternative provided was to download iTunes on laptop and connect iPhone and try to update iPhone iOS. But still says 7.1.2 current even though the iTunes on the laptop is a much later version 12.5.5.5?

Is there another way to update the iOS on the iPhone 4 so that we can install Skype on the iPhone?